1. Field of the Invention
The invention relates to a method of processing contaminated soils and similar materials, particularly from coke making locations, by removing, decontaminating and possibly replenishing the removal location with purified soil in such a manner that the removed soil is dried and comminuted in a mill through which hot gases flow, the solids/gas mixture is introduced into a cyclone separator and is there separated into gaseous and solid components; the solids are thermally treated at a high temperature, are then cooled and possibly employed to replenish the removal location; and, after being subjected to a cooling and filtering process, the exhaust gases are discharged, at least in part, to the atmosphere.
2. Background of the Related Art
It is known to excavate rivers in order to remove deposits therein and to introduce the material, after preprocessing it by comminuting it in a crusher and screening it, into a rotary kiln system. The rotary kiln system is composed of two series connected revolving drums, the first one of which operates as a drying drum to pre-dry the material. The second rotary kiln following in the stream of material is fired by an open flame which acts directly on the solids to be purified at temperatures between 400.degree. C. and 800.degree. C. The purified soil is removed from the rotary kiln and installed again at the location where it was obtained.
After the dust components contained therein have been removed, the exhaust gases generated in the rotary kiln system are heated in a combustion chamber equipped with a separate burner to about 1200.degree. C. and are thus decontaminated. After subsequent cooling and filtering, the purified exhaust gases are discharged to the atmosphere. Part of the exhaust gases are fed to the rotary drying drum to intensify the drying process and to improve the energy balance. The drawback noted in the prior art method is that the preprocessing by crushing and screening does not produce sufficiently small grain sizes in the contaminated material so that the subsequent drying process step is ineffective.
In the subsequent process step of directly charring the solids by a flame in the rotary kiln, there exists the additional drawback that uniform heating does not take place, rather streaks of cold gas develop which result in untreated streaks of solids in the discharged material, the latter thus being purified only insufficiently. Finally, the temperatures realized in a rotary kiln system are not sufficient to decompose all noxious substances so that the thus purified soil no longer meets present requirements for environmental protection. Also, the return of purified hot exhaust air to the drying drum through a branch provided downstream of the second burner is unfavorable from an energy engineering point of view.
German Laid-Open Patent Application 3,623,939 which corresponds to U.S. Pat. No. 4,750,436, discloses a method and an apparatus operating according to the method for processing contaminated soils and similar materials by removing, decontaminating and replenishing the removal location with purified soil, wherein the removed material, possibly after pre-processing, is dried and then thermally treated at a high temperature. In a mill through which hot gases flow, the drying is combined with comminution of the material to a grain size range from 0 to 10 mm in such a manner that a significant portion of the contaminants are transferred into the gas phase. After drying, the material together with the gas phase is treated in the form of a solids/gas dispersion in a burner-equipped heating and decontamination line at a temperature in a range between 800.degree. C. and 1200.degree. C. and is subsequently separated in a cyclone separator stage from the gas phase containing all of the noxious substances, with the gas phase being included in the circuit with the burner to completely decompose the noxious substances. A partial stream of the combustion gases is fed to the combined drying and comminution stage, while the purified solids are discharged after cooling. The cooling air is fed to the burner as preheated primary air.
The drawbacks of the prior art discussed are essentially that the circuitry of the system components only permits a combustion temperature, with respect to the solids, of a maximum of 800.degree. C. Periods of dwell of only two seconds are realized for the solids in the decontamination line. This relatively short passage time is only sufficient, however, to decontaminate a grain size range of &lt;3 mm at a temperature of 800.degree. C. so that the easily volatile components can be separated from the solid. For grain sizes above 3 mm, it may even happen that sufficiently thorough heating cannot be realized in this short period of passage, even to remove the easily volatilized components from the solid. Aromatic hydrocarbons, aliphatic hydrocarbons, cyanides, easily volatilized heavy metals, PCB's and chlorinated hydrocarbon cannot be removed during this short passage time and at these temperatures.
Another drawback is that the hot gas circulation between decontamination and burner is a stress for the fan employed. Moreover, the large quantity of dust in the separated gases also constitutes a strain on the burner, with the resulting percentage of filter dust to be disposed of making the process more expensive.
Based on German Laid-Open Patent Application 3,623,939, it is the object of the invention to provide an improved method, as well as apparatus, for processing contaminated soils and similar materials particularly from coke making locations, by removing, decontaminating and possibly replenishing the removal location with purified soil in such a way that the removed sol is dried and comminuted in a mill through which hot gases flow, the solids/gas mixture is introduced into a cyclone separator and is there separated into gaseous and solid components; the solids are thermally treated at a high temperature, are subsequently cooled and possibly employed to replenish the removal location; and at least part of the exhaust gases are discharged to the atmosphere after having undergone a cooling and filtering process, in that the flow path is decoupled without the gas being circulated between the decontamination line and the combustion chamber. In order to increase the flexibility, that is, the degrees of freedom of the combustion system so that substances, such as easily volatized heavy metals, PCB's, CHC and the like can be destroyed thermally, it is desirable to modify the combustion system. Also the atmosphere in the entire system should be as dust-free as possible to thus prevent the formation of a molten phase and clogging in the combustion chamber.